This invention relates generally to fuel injection control systems and, more particularly, to a control system for determining the start of fuel injection events in a multi-shot fuel injection signal for each cylinder of an engine wherein the main injection timing is preserved when the start of the injection event becomes too advanced.
Electronically controlled fuel injectors are well known in the art including both hydraulically actuated electronically controlled fuel injectors as well as mechanically actuated electronically controlled fuel injectors. Electronically controlled fuel injectors typically inject fuel into a specific engine cylinder as a function of an injection signal received from an electronic controller. These signals include waveforms that are indicative of a desired injection rate as well as the desired timing and quantity of fuel to be injected into the cylinders. Regulations pertaining to engine exhaust emissions are becoming increasingly restrictive throughout the world including, for example, restrictions on the emission of hydrocarbons, carbon monoxide, the release of particulates, and the release of oxides of nitrogen (NOx). Tailoring the number of injections and the injection rate of fuel to a combustion chamber, as well as the desired quantity and timing of such fuel injections, is one way in which to control emissions of an engine and meet such emission standards. As a result, multi-shot fuel injection techniques have been utilized to modify the burn characteristics of the combustion process in an attempt to reduce emission and noise levels. Multi-shot injection typically involves splitting the total fuel delivery to the cylinder during a particular injection event into two or more separate fuel injections generally referred to as a pilot injection, a main injection, and an anchor injection, which injections may each be referred to generally as a shot. As used throughout this disclosure, an injection event is defined as the injections that occur in a cylinder during one cycle of the engine. For example, one cycle of a four cycle engine for a particular cylinder, includes an intake, compression, expansion, and exhaust stroke. Therefore, the injection event in a four stroke engine includes the number of injections, or shots, that occur in a cylinder during the four strokes of the piston. The term shot as used in the art may also refer to the actual fuel injection or to the command current signal to a fuel injector or other fuel actuation device indicative of an injection or delivery of fuel to the engine. At different engine operating conditions, it may be necessary to use different injection strategies in order to achieve both desired engine operation and emissions control. For example, at higher engine speeds, the controllability of distinct fuel shots relative to each other in a multi-shot fuel injection signal is somewhat more difficult because of issues associated with high engine speeds. For example, if higher engine speeds are not accounted for, the total time duration of the fuel injection signal may decrease, whereby the time delay between the end of one fuel shot and the beginning of a subsequent fuel shot decreases. At significantly high engine speeds, the time delay may decrease below a minimum acceptable level, and the fuel shots may even overlap. This is disadvantageous to the performance, fuel efficiency, and emissions of the engine. Even with more advanced electronically controlled fuel injectors, during high speed engine operating conditions it is sometimes difficult to accurately control the timing of fuel delivery associated with each shot despite the use of electrical current control signals.
In a fuel control system having one driver or controller to control multiple injectors, it is desirable not to command injection signals to two injectors at the same time. The undesirability of generating simultaneous command signals to multiple injectors is due in part to the physical limitations of having a single driver. However, as engine operating conditions change, the number, timing, and duration of injection signals may vary to accommodate desired emissions and engine performance. Therefore, adverse system performance may result if the overall injection timings of the cylinders are not dynamically monitored to avoid injection collisions.
Accordingly, in a system in which multiple fuel injections and different injection waveforms are achievable, it is desirable to control the delivery of individual fuel shots in each fuel injection event so as to minimize overall emissions and fuel consumption of the engine.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, there is disclosed an electronically controlled fuel injection system capable of delivering fuel injection signals, including a plurality of fuel injection shots, to the cylinders of an internal combustion engine during a single fuel injection event. The system includes at least one fuel injection device, such as a fuel injector, associated with each cylinder and operable to deliver the multiple fuel shots, and a controller operable to determine the timing and actual amounts of fuel for each shot.
In one embodiment of the present invention, the controller is operable to provide fuel injection signals comprising three distinct fuel shots, namely a pilot shot, a main shot, and an anchor shot. Each fuel injection signal corresponds to a particular cylinder in an engine. The controller is further operable to determine a desired start time for the pilot shot, and an angular position of the piston that corresponds to such desired start time for the pilot shot, for each fuel injection event.
For a particular cylinder in the engine, the controller is operable to convert that cylinder""s timing trim to an angle. The controller thereupon determines a relative injection angle of the first shot, e.g., pilot shot, for the cylinder, which angle is the sum of the cylinder""s timing trim angle, its advanced pilot timing angle, and its main shot timing angle. If the determined relative injection angle is greater than a predetermined threshold value for the maximum relative injection angle allowed for that cylinder, then the controller is operable to set the relative injection angle of that cylinder to its maximum allowable relative injection angle. The controller can thereupon determine that cylinder""s absolute injection angle for the respective fuel injection event by adding the cylinder""s top dead center offset value, which offset value is a predetermined known value available to the controller, to the cylinder""s relative injection angle. The controller then updates the cylinder""s absolute injection angle value with the absolute injection angle value thus determined. The controller is operable to perform these steps in a loop for each cylinder in the engine for each fuel injection event, and the entire procedure is thereafter repeated for subsequent fuel injection events.